Loughborough student Tancock produced a fine swim

The 21-year-old Tancock finished with a time of 53.61 seconds to give Britain their first pool medal of the event.

The race was won in 52.98 seconds by Aaron Peirsol, one of three Americans who set new world records on Tuesday.

Michael Phelps set a new mark in the 200m freestyle while Natalie Coughlin secured a new 100m backstroke record.

Interview: British swimmer Liam Tancock

606: DEBATE Phelps was awesome - he really got the record by absolutely killing it on the turns - his underwater work is amazing BK

Italy's Federica Pellegrini also got in on the act, setting a new 200m freestyle record with a time of 1:56.47 seconds in the semi-final.

She wiped 0.17 seconds off the previous record of 1:56.64 set by Franziska van Almsick of Germany in 2002.

Britain's Caitlin McClatchey qualified for the 200m freestyle final with the seventh quickest time of 1:57.86. Melanie Marshall missed out after coming fifth.

Michael was incredible and Natalie did well so I had to do something too Aaron Peirsol

Phelps recorded a time of 1:43.86 seconds to beat the previous record of 1:44.06 set by Australian Ian Thorpe in Japan in 2001.

The 21-year-old was helped by a blistering start which saw him lead rival Pieter Van Den Hoogenband after the 50m in a world record time. He pulled away from the Dutchman coming off the wall at 150m and moved out to a body-length lead.

"I felt awesome. I haven't seen the splits but I did what I wanted and now the ball is rolling," said Phelps, who helped secure the United States' first gold of the championships in the 4x100m freestyle relay on Sunday.

"I just wanted to take it out tonight and knew the biggest key was to get out after the first 100m. That's all I wanted to do and try to make a step on the third 50m and by then it's all adrenaline."

Van den Hoogenband took silver in 1:46.28 with Park Tae-hwan of South Korea taking bronze.

Coughlin has broken a minute in the 100m backstroke five times

Coughlin beat her own world record as she claimed the 100m backstroke title. She finished in a time of 59.44, beating her previous best of 59.58 which she set in 2002.

"It has been a goal of mine for five years now to break my best," she said.

"I felt really strong and confident. I knew that was exactly how I needed to swim that race to break the record and I did."

Laure Manaudou of France finished second in 59.87 to become only the second woman to break a minute for the event. Japan's Reiko Nakamura finished third.

Peirsol beat his own mark of 53.17 set in April 2005 and is the only swimmer to have won the event three times and at three consecutive world championships.

"I think it's the most impressive team I've ever been on," he said. "Michael was incredible and Natalie did well so I had to do something too."

Australia's Leisel Jones posted the second fastest time in history to defend the 100m breaststroke final title she won in Montreal two year's ago. She recorded a time of 1:05.72 to finish ahead of America's Tara Kirk and Ukraine's Anna Khlistunova.

Scotland's Kirsty Balfour missed out on a medal after finishing fifth. The 23-year-old, who had qualified fourth fastest, was last at the turn but recovered to clock a time of 1:08.05.

The United States won their third gold medal of the night when Kate Ziegler finished first in the 1500m in a time of 15:53.05.